Serial paedophile and former priest Brian Joseph Spillane​ has been sentenced to another 13 years in jail for abusing young boys, many of whom were homesick and turned to him for help, at a private Catholic boarding school.

Spillane, 74, kept his back turned to his victims and their families as the sentence was handed down in a packed court room in the Downing Centre District Court on Thursday.

The former teacher, chaplain and head of discipline at St Stanislaus' College, Bathurst, in central west NSW preyed on young boys who came from strictly Catholic families who revered priests.

Spillane used religious rituals, purporting to perform exorcisms, prayers and to speak in tongues, as a ruse to sexually abuse the boys.

After two trials last year, Spillane was found guilty of a total of 16 charges, including sexual assault, indecent assault and buggery, relating to attacks on several boys between 1974 and 1990.

The boys were aged between 12 and 15 and were either boarders or day students at the school.

He knew that most of these complainants were desperately homesick and offered them comfort only to sexually abuse them," Judge Robyn Tupman said.

"He knew he could act with impunity and with almost no chance that his behaviour would be revealed."

Spillane was first taken into custody for child sex offences in 2010 and has faced a string of trials.

He was found guilty of abusing more than 30 children over a period of nearly 30 years. The victims were both boys and girls, and the offences were not all linked to St Stanislaus'.

He was serving a sentence of at least 11 years for those offences.

On Thursday, Judge Tupman sentenced him to a further maximum sentence of 13 years with a non-parole period of nine years.

As the sentences will run partially concurrently, Spillane's eligible release date has been extended by five years to 2026.

"There is a prospect that he will die in prison," Judge Tupman said.

"Even if he survives jail, when he does emerge on parole, he will be an old man."

"It is unlikely that there was not one person at St Stanislaus' that had not noticed what this offender had been doing for almost 20 years," Judge Tupman said

Spillane told one of his victims, aged 13, that he had the devil in him and purported to perform an "exorcism" on him by masturbating him.

He gave another of his victim, aged 15, medication to make him drowsy before he sexually abused him. Spillane was the school's dean of discipline when he raped another 15-year-old boy.

He arranged candle-lit "prayer meetings" at night with his pupils during which he claimed to start speaking in tongues, trying to induce in them a trance-like state in order to sexually abuse them.

"These were impressionable teenage boys all boarders all away from their homes so without any independent sounding board to check this behaviour against," Judge Tupman said.

After leaving the school, Spillane worked at a suburban parish in Sydney before he left the church in 2004.

A suppression order had been in place covering Spillane's crimes and the name of the boarding school, known as "Stannies", until last year after two more jury trials were completed.